length

Lengths are measurements between the extreme points of any pathway, object, or defined part of an object. They are usually taken in a straight line parallel to the mean surface of the earth, except when measuring a diagonal line or the length of a travel route. These include measurements under the names of length, width, span, and similar headings.

Lengths are measured in the same units as height, depth, thickness, and elevation.

A route length follows the defined path, so a curved route can exceed the straight separation of its endpoints. A width or span uses its own stated direction and endpoints within the same family of length units.